Substance P is a naturally occurring undecapeptide belonging to the tachykinin family of peptides, the latter being so-named because of their prompt contractile action on extravascular smooth muscle tissue. The tachykinins are distinguished by a conserved carboxyl-terminal sequence. In addition to substance P, the known mammalian tachykinins include neurokinin A and neurokinin B. The current nomenclature designates the receptors for substance P, neurokinin A, and neurokinin B as neurokinin-1 (NK-1), neurokinin-2 (NK-2), and neurokinin-3 (NK-3), respectively. Tachykinin, and in particular substance P, antagonists are useful in the treatment of of clinical conditions which are characterized by the presence of an excess of tachykinin, in particular substance P, activity, including disorders of the central nervous system, nociception and pain, gastrointestinal disorders, disorders of bladder function and respiratory diseases. Attempts have been made to provide antagonists for the receptors of substance P and other tachykinin peptides in order to more effectively treat the various disorders and diseases mentioned above. For example, U.S. Pat. Nos. 5,387,595, 5,750,549, 5,877,191, 6,479,518 and Bioorg. & Med. Chem. Lett., 1345 (1995) disclose certain compounds as tachykinin receptor antagonists.